Radial and horizontal magnetic-head-positioning mechanism

ABSTRACT

A magnetic-head-positioning assembly useful in a magnetic disc storage system. The positioning assembly is comprised of a linear motor coupled to a linearly movable carriage assembly including a mounting yoke. An arm set assembly is secured to the yoke for linear movement therewith. The arm set assembly is comprised of a backplate fixed to the yoke and a plurality of arm assemblies carried by the backplate. Each arm assembly includes a frame carrying one or more magnetic head assemblies and a cam rod linearly movable with respect to the head assemblies. Linear movement of the cam rod in a forward direction forces the magnetic heads to a landed position in which they are able to closely fly over a disc surface and cam rod movement in a rearward direction allows the heads to move away from the disc surface to an unlanded position. The cam rods are all tied to an arm set tie bar which is supported on the backplate for linear movement with respect thereto between a retracted position (heads unlanded) and an extended position (heads landed). Movement of the tie bar toward the extended position is opposed by a pair of springs which urge the tie bar toward the retracted position. Latching means are provided to latch the tie bar either in the extended or retracted position. The latching means are electrically controlled with electrical power being required both to release the tie bar for forward movement from the retracted position and to retain the tie bar latched in the extended position.

United States Patent [72] Inventors Clarence Huetten Woodland Hills; 1 Jerome W. Gibson, Van Nuys, both of Calif. [21] Appl. No. 98,986 [22] Filed Dec. 17, 1970 [45] Patented Jan. 11, 1972 [7 3] Assignee Data Products Corporation Woodland Hills, Calif.

[54] RADIAL AND HORIZONTAL MAGNETIC-HEAD- Primary Examiner-Bernard Konick Assistant Examiner-Vincent P. Canney Attorney -Lindenberg, Freilich & Wasserman ABSTRACT: A magnetic-head-positioning assembly useful in a magnetic disc storage system. The positioning assembly is comprised ofa linear motor coupled to a linearly movable carriage assembly including a mounting yoke. An arm set assembly is secured to the yoke for linear movement therewith. The arm set assembly is comprised of a backplate fixed to the yoke and a plurality of arm assemblies carried by the backplate. Each arm assembly includes a frame carrying one or more magnetic head assemblies and a cam rod linearly movable with respect to the head assemblies. Linear movement of the cam rod in a forward direction forces the magnetic heads to a landed position in which they are able to closely fly over a disc surface and cam rod movement in a rearward direction allows the heads to move away from the disc surface to an unlanded position. The cam rods are all tied to an arm set tie bar which is supported on the backplate for linear movement with respect thereto between a retracted position (heads unlanded) and an extended position (heads landed). Movement of the tie bar toward the extended position is opposed by a pair of springs which urge the tie bar toward the retracted position. Latching means are provided to latch the tie bar either in the extended or retracted position. The latching means are electrically controlled with electrical power being required both to release the tie bar for forward movement from the retracted position and to retain the tie bar latched in the extended position.

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sum 3 o 3 N VENT 0/25 LARENCE //U7T/V JEROME l4- GIBSON w h wldw A 770/?NEY5 BACKGROUND OF THE INVENTION 1. Field of the Invention:

This invention relates generally to magnetic disc data storage systems, and more particularly, to an assembly useful for positioning magnetic heads in such a storage system.

2. Description of the Prior Art:

Magnetic disc storage units are extensively used in dataprocessing systems for storing large amounts of data. They generally include a plurality of disks each having a pair of magnetic recording surfaces. Magnetic heads are supported adjacent to the disk surfaces for writing information on and reading information from the discs. In order to achieve highrecording densities, it is necessary to locate the heads as closely as possible to the disc surfaces. Generally, this is accomplished by providing a suitable hydrodynamic head design which permits the head pad to fly just above the disc surface on a thin air bearing which may have a thickness on the order of 100 microinches. The air bearing is produced as a consequence of disc surface movement and generally, with most known designs, if the disc surface velocity decreased to below a certain rate while the heads were flying, the heads would crash into and damage the disc surface. In view of this potentiality, it is common practice for a head support means to be able to selectively support the head either in a landed position in which the head is able to fly close to the disc surface on the air bearing or in an unlanded position in which the head is spaced from the disc and supported independently of disc motion.

In order to minimize the electronic hardware and number of heads required in any particular system, .it is also common practice to support the heads on arms which are radially movable with respect to the disc surface. In this manner, a considerably fewer number of heads than tracks per surface are required. For example, in a typical system, 800 tracks may be defined on a disc surface with only two heads being provided per surface. Such an arrangement of course requires that the arms be mounted so as to be precisely and rapidly movable along a disc radius in order to be able to bring a head into alignment with a desired track.

SUMMARY OF THE INVENTION The present invention is directed to an improved head-positioning assembly which operates to automatically reposition heads to an unlanded position in the event of electrical power failure, or other occurrence, to thus reduce the likelihood of a head to disc collision.

More particularly, in accordance with the preferred embodiment of the invention, the heads are latched in a landed position by the action of an energized solenoid. A spring means is provided with acts to urge the heads to an unlanded position and thus, upon loss of electrical power, the heads will be unlatched from the landed position allowing the spring means to reposition the heads to the unlanded position.

In accordance with a significant feature of the invention, automatic repositioning to the unlanded position can occur at any time regardless of the track location of the heads. That is, in contrast to some prior art systems, it is not necessary to reposition the arms to a particular track location in order to unland the heads. Rather, the heads can be automatically unlanded from any track location.

In accordance with the preferred embodiment of the invenmovement of the cam rod in a forward direction forces the magnetic heads to a landed position in which they are able to closely fly over a disc surface and cam rod movement in a rearward direction allows the heads to move away from the disk surface to an unlanded position. The cam rods are all tied to an arm set tie bar which is supported on the back plate for linear movement with respect thereto between a retracted position (heads unlanded) andan'extended position (heads landed). Movement of the tie bar toward the extended position is opposed by a pair of springs which urge the tie bar toward the retracted position. Latching means are provided to latch the tie bar either in the extended or retracted position. The latching means are electrically controlled with electrical power being required both to release the tie bar for forward movement from the retracted position and to retain the tie bar latched in the extended position. Thus, loss of electrical power will unlatch the tie bar and permit the springs to unland the heads.

The novel features of the invention are set forth with particularly in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a magnetic-head-positioning assembly in accordance with the present invention;

FIG. 2 is a side view of the head-positioning assembly, in accordance with the present invention;

FIG. 3 is a fragmentary plan view of the head-positioning assembly in accordance with the present invention;

FIG. 4 is a front view of the linear motor of FIG. 1 illustrating the two positions of a solenoid-actuated interposer;

FIG. 5 is a sectional view taken substantially along the plane of 55 of FIG. 2 illustrating particularly the relationship between the backplate, tie bar, and latch member of the arm set subassembly of the head-positioning assembly;

FIG. 6 is a sectional view taken substantially along the plane 6- 6 illustrating the tie bar latched in the retracted position;

FIG. 7 is a plan view taken substantially along the plane 7 7 of FIG. 5 also illustrating the tie bar latched in the retracted position;

FIG. 8 is a plan view similar to FIG. 7 except illustrating the tie bar latched in the extended position; and

FIG. 9 is a sectional view taken substantially along the plane 99 of FIG. 8 also illustrating the tie bar latched in the extended position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is now called to FIG. 1 of the drawing which illustrates a fragmentary portion of a magnetic disc storage unit and, more particularly, a magnetic-head-positioning assembly in accordance with the present invention. The magnetic disc storage unit includes a plurality of discs 10 stacked on and affixed to a common hub 12. The hub is supported for rotation in a conventional manner and is driven by a motor (not shown).

As is well known in the art in order to achieve a relatively high-density low-cost magnetic disc storage unit, it is common practice to utilize movable heads which can be selectively positioned over any one of a plurality of concentric tracks defined on the surface of a disc. For example only, a typical 24-inch diameter disc may have on the order of 800 different concentric tracks defined on a surface thereof. In order to minimize cost, as few as one positionable head per surface may be utilized. Higher data access speeds can, of course, be achieved by increasing the number of heads per disc surface. In the exemplary embodiment of the invention to be disclosed herein, it will be assumed that two heads are provided per disc surface but it should be understood that any number of heads can be utilized consistent with the teachings of the present invention.

In a typical embodiment of the present invention, the heads are carried by arm assemblies 14, with a group of such arm assemblies contained within a common arm set assembly 16. As will be better appreciated hereinafter, each arm assembly 14 preferably carries back-to-back heads, as for example is disclosed in application, Ser. No. 53,828 filed July 8, 1970, by Clarence Huetten and entitled Magnetic Disc Head Assembly so as to enable data to be read from the opposed surfaces of spaced discs using only a single arm assembly. That is, in the preferred embodiment, all of the disc surfaces other than the top and bottom surfaces in the stack can be read using a number of arm assemblies equal to one less than the number of discs since the back-to-back heads on each arm assembly operate on opposed disc surfaces. In order to read both the top and bottom stack surfaces, two additional arm assemblies are provided.

As previously mentioned, the arm assemblies 14 illustrated in FIG. 1 all constitute part of a common arm set assembly 16 which is mounted for linear movement toward and away from the axis or hub 12 of the disc stack. As will be seen, the arm set assembly 16 is analogous to a comb in which the arm assemblies 14 correspond to the comb teeth. All of the arm assemblies 14 are fixed relative to one another and move together toward and away from the disc stack axis.

The arm set assembly 16 is preferably fixed to a mounting yoke 18 of a carriage assembly 20. The carriage assembly 20 includes a plurality of rods 22 which carry roller bearings 24 engageable with fixed rails 26. The carriage assembly 20 forms part of a linear motor 28, for example, of the type described in detail in application, Ser. No. 71,013, filed on Sept. 10, 1970, by Clifford Helms et al. and entitled Linear Positioner." Although said application Ser. No. 71,103 discloses a linear motor particularly well suited for use with embodiments of the present invention, it should be understood that the practice of the present invention does not require any particular linear motor. Rather, any linear motor exhibiting sufficient speed and precision for the intended application can be employed. Precision positioning is of course essential in typical applications where, for example, track densities as great as 150 tracks per inch may be required. In addition, motor speed is generally highly significant because positioning time constitutes a significant portion of the overall memory access time.

From what has been said thus far, it should now be appreciated, that the arm set assembly 16 including a plurality of forward projecting arm assemblies 14 can be linearly moved by motor 28 along a disc radius for precise positioning of the heads 15 adjacent to any selected track. In order to achieve high-recording densities, it is not sufficient to merely achieve high-track density per radial inch, but it is also necessary to achieve high-bit density per track inch. In order to achieve such high-bit density, it is readily known that the heads must be operated extremely close to the disc surface. In order to assure this, it is common practice in the art to utilize head assemblies having hydrodynamically designed head-carrying pads which permit the head pad to fly just above the disc surface on a thin air bearing which may have a thickness on the order of I microinches. The air bearing is produced as a consequence of disc surface movement. Generally, with most known head designs, if the disc surface velocity was to be reduced below a certain rate while the heads were flying, the heads would collide with the disc surface and cause damage to both the disc and the head. In view of this potentially, it has become common practice to configure the head assemblies such that the head can be selectively supported in either a landed position in which the head can fly close to the disc surface on the air bearing or in an unlanded position in which the head is spaced from the disc surface and supported independently of disc motion.

The aforementioned application Ser. No. 53,828, discloses a head assembly configuration in which a linearly movable cam rod is employed to force the head to a landed position for flying close to the disc surface. That is, as is disclosed in detail therein, when the cam rod is moved forwardly relative to the head assembly, the cam surface on the rod forces the head toward a landed position close to the disc surface. When the cam rod is moved rearwardly, the head returns to the unlanded position spaced from the disc surface.

The present invention is directed to a head-positioning assembly useful in cooperation with head-carrying arms of the type disclosed in said application, Ser. No. 53,828, in which a linearly movable cam rod controls the position of the head. In accordance with a primary feature of the head-positioning assembly of the present invention, the heads are automatically retracted to an unlanded position in the event of a catastrophic failure such as loss of electrical power. Automatic unlanding of the heads, in accordance with the present invention, is able to occur at any location of the arms relative to the discs. More specifically, in accordance with the present invention, there is no need to return the heads to any particular track location for unlanding.

Attention is now called to FIGS. 2 and 3 of the drawing which illustrate a preferred head-positioning assembly in accordance with the invention particularly adapted for use with head-carrying arm configurations of the type disclosed in the aforementioned application, Ser. No. 53,828. Note that the arm assembly 14 consists of a substantially rectangular frame 30 which carries back-to-back magnetic head assemblies 15A and 158. The frame 30 also carries a cam rod 32 which is mounted for linear movement with respect to the frame 30. The cam rod 32 is provided with cam surfaces 34 disposed so as to engage and ride on follower buttons 36 forming part of the magnetic head assemblies 15. By moving the cam rod 32 to the right, as illustrated in FIG. 2 and FIG. 3, the buttons 36 of the head assembly 15 will be forced outwardly, i.e., away from the longitudinal centerline of the frame 30 to a landed position adjacent to the disc surfaces, as is disclosed in detail in said application, Ser. No. 53,828. Subsequent return of the cam rod 32 to the position illustrated in FIGS. 2 and 3 allows the return of the head assemblies 15 to the unlanded position illustrated.

In accordance with the present invention, the arm set assembly includes a front plate 40 fixedly secured by upper and lower pins 42, 44 to a backplate 46. The backplate 46 is in turn securely mounted, as by screws, to the previously mentioned carriage assembly yoke 18. The arm assembly frames 30 are all fixedly secured to the back plate 46.

The arm set assembly further includes a channel-shaped tie bar having legs 50A and 50B projecting forwardly from a base member 50C. A cylinder member 52 is secured to the tie bar 50 and projects rearwardly thereof. The cylinder member 52 extends through, and is slidable in a guide member 53 attached to the backplate 46 and having an opening 54 therein aligned with an opening through the backplate 46. Moreover a pair of coil springs 56 and 58 (FIG. 7) extend between the tie bar 50 and the fixed front plate 40. As is best shown in FIG. 7, the springs 56 and 58 fit into and are retained in cup receptacles 60 formed on the rear side of the front plate 40. The rear ends of the springs 56 and 58 are preferably retained in the channel-shaped tie bar 50 by slots 62 formed in both the top and bottom legs 50A and 50B of the tie bar. As should be apparent, the springs 56 and 58 act to urge the tie bar 50 rearwardly into the vicinity of the backplate 46 to the position illustrated in FIGS. 2 and 7, for example.

The cam rods 32 on all of the arm assemblies 14 have hooks 70 (FIG. 3) on their rear ends which hook around pins 72 carried by the tie bar 50. Thus, when the tie bar 50 is in the retracted position adjacent to the backplate 46 as shown in FIGS. 2 and 7, the cam rods 32 are also in the retracted position, as shown in FIG. 3. From what has previously been said, it will be recalled that then the cam rod 32 is in the retracted position, the head assemblies 15 are in the unlanded position.

It is pointed out that in the preferred embodiment of the invention, the arm set front plate 40 actually constitutes a circuit board for transferring information to and from the head assemblies carried by the am assembly frames 30. In addition,

each arm assembly 14 preferably also carries a circuit board 63 for providing communication channels between the head assemblies and front plate circuit board 40.

In order to assure that the heads are indeed unlanded when they are intended to be unlanded, a latch means 741 is provided for latching the tie bar in the retracted position illustrated in FIGS. 2 and 7. The latch means 748 includes a latch member 76 mounted for pivotal movement about the pin 78. The latch member 76 includes an upper latching arm 80 and a lower latching arm 82 as well as a lever arm 84. A spring 86 normally urges the latch member 76 clockwise for projecting the freeend of the upper latching arm 80-into a space 90 between the forward end of the cylinder member 52 and the rear surface of the tie bar 50 base member 50C. That is, when the tie bar is in the retracted position of FIGS. 2 and 7 held against the backplate 46, the upper latching arm 80 of the latch member 76 is normally urged by the spring 86 into the space 90 between the cylinder'member 52 and the tie bar 50 so as to prevent forward movement of the cylinder member 52 relative to the backplate 46.

In order to enable the tie bar 50 to be moved out of the retracted position of FIGS. 2 and 7 to the extended position of FIGS. 8 and 9, the latch member 76 must be rocked counterclockwise. This is accomplished by a downward movement (FIG. of the center cable 92 of a jacketed control cable 94. The cable 92 is aligned with the lever arm 84- and downward movement of the cable 92 rocks the latch member 76 in a counterclockwise direction to move the upper latching arm 80 out of the space 90 (FIG. 9) forward of the cylinder member 52. The cable 92 is controlled by a solenoid 96 (FIG. vll) which can be mounted on the motor housing.

Once the upper latching arm 80 moves out of the space 90 forward of the cylinder member 52, the cylinder member and tie bar 50 are free to move forward relative to the backplate 46 in opposition to the urging of springs 56 and 58. In accordance with the preferred embodiment of the invention, the tie bar 50 is forced forward to the extended position by an electrically controlled interposer 100 (FIG. 2) which projects through a slot in the backplate 46 and bears against the rear surface of the tie bar 50 as the carriage assembly is drawn rearwardly by the linear motor 28. More particularly, the interposer means 100 consists of an interposer spindle 102 carried on the free end of an arm 1041. A second end of the arm 104 is terminally secured to a rod 106 which extends through the center of the motor 28 and is coupled to a solenoid 108. Energization of the solenoid 108 rotates the rod 106 to move the interposer spindle 102 from the full line position shown in FIGS. 2 and 4 to the dotted line position illustrated therein. When the interposer spindle 102 is in thefull line position of FIGS. 2 and'4, it is aligned with the lower open end 110 of a slot 112 (FIG. 5) formed in the backplate 46. On the other hand, when the interposer spindle 102 is moved to the dotted line position in FIGS. 2 and 4, it is alignedwith the rear surface of the tie bar base member 500. Thus, by energizing the solenoid 108 to move the interposer spindle 102 to the dotted line position in FIGS. 2 and 4 and by then controlling the linear motor 28 so as to draw the carriage assembly 20 rearwardly, the interposer 102 will project through the backplate slot 112 to engage the tie bar 50. When the interposer solenoid 108 is energized to move the interposer spindle to the dotted line position, the latch solenoid 96 is also energized to rock the latch member 76 to the counterclockwise position to unlatch the tie bar 50. As a consequence, as the linear motor draws the carriage assembly rearwardly, the interposer spindle 102 will bear against the rear surface of the tie bar 56 to project it forwardly relative to the backplate 46.

The cylinder member 52 secured to the back surface of the tie bar 50 is provided with a slot 120 of the underside thereof. As the interposer spindle 102 moves the tie bar 50 forwardly relative to the backplate 46 as the carriage assembly is drawn rearwardly, the slot 120 moves into alignment with the lower latching arm 82 of the latch member 76. As long as the solenoid 96 remains energized to maintain the cable force against the lever arm 84, the latch member 76 will pivot further counterclockwise when the slot 120 moves into alignment with the lower latching arm 82. As a consequence, this action will latch the cylinder member 52 and the tie bar 50 connected thereto in a forward extended position as shown in FIGS. 8 and 9.

Forward movement of the tie bar to the extended position of FIGS. 8 and 9 of course forces the cam rods 32 of the arm assemblies 141 to a forward extended position which in turn forces the magnetic head assemblies 15 to a landed position. Thus, for so long as the tie bar 50 remains latched in the extended position in FIGS. 8 and 9, the head assemblies will be in a landed position. Once the tie bar 50 has been latched in the extended position, the interposer solenoid 108 is deenergized to permit the interposer spindle 102 to move back to the full line position in FIGS. 2 and 4. Thereafter, the carriage assembly is free to move over its entire range to locate the landed heads in alignment with any track. With the interposer solenoid deenergized, the interposer spindle 102 will merely project through the lower end ll 10 of backplate slot 112 as the carriage assembly is drawn toward the zero track location.

It will be appreciated that the latch member 76 remains in its fully counterclockwise position only so long as cable 92 continues to apply force to the lever arm 84 to force the lower latching arm 82 against the spring urging of spring 86, into the cylinder member slot 120. As soon as the interposer solenoid 96 is deenergized, the cable 92 is withdrawn to thus permit the spring 86 to pivot the latch member 76 clockwise to thereby withdraw the latching arm 82 from the cylinder member slot 120. This in turn allows the compressed springs 56 and 58 to drive the tie bar 50 back to the retracted position against the backplate 46 in which it immediately becomes latched as the upper latching arm moves into the space 90 forward of the cylinder member 52.

Thus, from the foregoing, it should now be recognized that a head'positioning assembly has been disclosed herein for use in a magnetic disc storage unit which provides for the latching of heads in a landed position and the automatic unlatching of the heads from the landed to an unlanded position upon the deenergization of a latch solenoid 96. Deenergization of the latch solenoid 96 will of course occur in response to electrical power failure but could also occur in response to the detection of any one of several other programmed conditions. It should be recognized that unlatching of the heads from the landed position will occur at any track location. That is, in accordance with the teachings of the present invention, there is no need to return the heads to a fixed home location in order to unland them. Rather, the present invention permits the heads to be unlanded at any track location thereby minimizing the possibility of head and disc damage.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

What is claimed is:

1. A magnetic disc storage system comprising a plurality of spaced magnetic discs secured to a common hub mounted for rotation about the axis thereof; and

a head-positioning assembly supported adjacent to said discs and including a plurality of magnetic heads each adapted to closely fly over the surface of a disc for writing data thereon and reading data therefrom, said assembly including:

a carriage mounted for linear movement;

a linear motor coupled to said carriage for imparting linear "motion thereto;

a plurality of arm assemblies each including a frame carrying one or more magnetic heads positionable in either an unlanded or landed position and cam means mounted on said frame movable from a first position to a second position in which said cam means bears against said heads and forces them into said landed position;

means mounting said arm assemblies on said carriage for movement therewith;

spring means urging said cam means to said first position; member to engage said latch arm in said receptacle. means for forcing said cam means against said spring means 8. The system of claim 7 including spring means acting on urging to said second position; and said latch member for disengaging said latch arm from said electrically actuatable latching means for latching said cam receptacle.

means in said second osition whereby deacmarion of 9. A head-positioning assembly useful in a magnetic disk said latching means permits said spring means to move 5101186 System, Said assembly including! said cam means to said first position to reposition said abackplate mounted for lineal movement; heads to said unlanded iti a tie bar mounted on said backplate for movement with 2. The system of claim 1 wherein said means for forcing said W thereto between a ren'acted Position and an cam means includes an interposer supported for movement tended Position; between a fi position aligned with Said cam means and a a plurality of arm assemblies, each including a frame carrying one or more magnetic head assemblies positionable in either an unlanded or landed position and cam means mounted on said frame movable from a retracted position second position misaligned with said cam means; and

electrically actuatable means for selectively moving said interposer to said first position whereat said linear motor can move Said carriage o draw Sal-d cam means against l5 to an extended position in which said cam means bears Said imerposer against said head assemblies and forces them into said landed position;

3. The system of claim 1 wherein said head-positioning assembly further includes a backplate fixedly secured to said carriage for movement therewith; and

a tie bar mounted on said back plate for linear movement with respect thereto between a retracted position and an extended position; and wherein said means mounting said arm assemblies includes means means securing said arm assembly frames to said backplate; means securing said cam means to said tie bar; spring means for urging said tie bar to said first position;

means for forcing said tie bar against said spring means to said extended position; and electrically actuatable latching means for latching said tie bar in said extended position whereby deactivation of said fixedly said arm assembly frames relative to Said 2 5 latching means permits said spring means to move said tie backplate and said am cam means W said tie ban bar to said retracted position to thus reposition said head 4. The system of claim 3 wherein each of said cam means assemblies to i unlanded position comprises an elongated rod having first end Connected) 10. The head-positioning assembly of claim 9 wherein said said tie bar; means for forcing said tie bar includes an interposer supported said rod having a head'engaging surface including a raised for movement between a first position aligned with aid tie bar Portion and a recessed Portion and a second position misaligned with said tie bar; and 5. The system of claim 3 wherein said means for forcing said electrically actuatable means for selectively moving said incam means includes an interposer supported for movement terposer to said first position whereby said backplate can between a first position aligned with said tie bar and a second be drawn toward said interposer to engage said interposer position misaligned with said tie bar; and and tie bar for moving said tie bar to said extended posielectrically actuatable means for selectively moving said intion relative to said backplate.

terposer to said first position whereat said linear motor 11. The head-positioning assembly of claim 10 wherein said can move said carriage to draw said tie bar against said inlatching means includes means secured to said tie bar defining terposer. a latch arm receptacle; 6 The system f lai 3 herein aid lat hi g means i a latch member, having a latch ann, mounted for pivotal eludes means secured to said tie bar defining a latch arm movement; and receptacle; electrically responsive means for pivoting said latch a latch member, having a latch arm, mounted for pivotal member to engage Said latch in Said receptacle when movement; d said tie bar is in said extended position. electrically responsive means for pivoting said latch head P i y of claim 11 whereillsaid member to engage said latch arm in said receptacle when electrically responsive means includes a control cable having a said tie barisin said extended position. jacket and a central cable therein and movable with respect 7. The system of claim 6 wherein said latch member inthereto; and

means mounting said control cable with said central cable cludes a lever arm; and wherein I engaged with said latch member.

said electrically responsive means includes a movable element engaged with said lever arm for pivoting said latch 1v r 

1. A magnetic disc storage system comprising a plurality of spaced magnetic discs secured to a common hub mounted for rotation about the axis thereof; and a head-positioning assembly supported adjacent to said discs and including a plurality of magnetic heads each adapted to closely fly over the surface of a disc for writing data thereon and reading data therefrom, said assembly including: a carriage mounted for linear movement; a linear motor coupled to said carriage for imparting linear motion thereto; a plurality of arm assemblies each including a frame carrying one or more magnetic heads positionable in either an unlanded or landed position and cam means mounted on said frame movable from a first position to a second position in which said cam means bears against said heads and forces them into said landed position; means mounting said arm assemblies on said carriage for movement therewith; spring means urging said cam means to said first position; means for forcing said cam means against said spring means urging to said second position; and electrically actuatable latching means for latching said cam means in said second position whereby deactuation of said latching means permits said spring means to move said cam means to said first position to reposition said heads to said unlanded position.
 2. The system of claim 1 wherein said means for forcing said cam means includes an interposer supported for movement between a first position aligned with said cam means and a second position misaligned with said cam means; and electrically actuatable means for selectively moving said inTerposer to said first position whereat said linear motor can move said carriage to draw said cam means against said interposer.
 3. The system of claim 1 wherein said head-positioning assembly further includes a backplate fixedly secured to said carriage for movement therewith; and a tie bar mounted on said back plate for linear movement with respect thereto between a retracted position and an extended position; and wherein said means mounting said arm assemblies includes means fixedly securing said arm assembly frames relative to said backplate and said arm cam means to said tie bar.
 4. The system of claim 3 wherein each of said cam means comprises an elongated rod having a first end connected to said tie bar; said rod having a head-engaging surface including a raised portion and a recessed portion
 5. The system of claim 3 wherein said means for forcing said cam means includes an interposer supported for movement between a first position aligned with said tie bar and a second position misaligned with said tie bar; and electrically actuatable means for selectively moving said interposer to said first position whereat said linear motor can move said carriage to draw said tie bar against said interposer.
 6. The system of claim 3 wherein said latching means includes means secured to said tie bar defining a latch arm receptacle; a latch member, having a latch arm, mounted for pivotal movement; and electrically responsive means for pivoting said latch member to engage said latch arm in said receptacle when said tie bar is in said extended position.
 7. The system of claim 6 wherein said latch member includes a lever arm; and wherein said electrically responsive means includes a movable element engaged with said lever arm for pivoting said latch member to engage said latch arm in said receptacle.
 8. The system of claim 7 including spring means acting on said latch member for disengaging said latch arm from said receptacle.
 9. A head-positioning assembly useful in a magnetic disk storage system, said assembly including: a backplate mounted for linear movement; a tie bar mounted on said backplate for movement with respect thereto between a retracted position and an extended position; a plurality of arm assemblies, each including a frame carrying one or more magnetic head assemblies positionable in either an unlanded or landed position and cam means mounted on said frame movable from a retracted position to an extended position in which said cam means bears against said head assemblies and forces them into said landed position; means securing said arm assembly frames to said backplate; means securing said cam means to said tie bar; spring means for urging said tie bar to said first position; means for forcing said tie bar against said spring means to said extended position; and electrically actuatable latching means for latching said tie bar in said extended position whereby deactivation of said latching means permits said spring means to move said tie bar to said retracted position to thus reposition said head assemblies to said unlanded position.
 10. The head-positioning assembly of claim 9 wherein said means for forcing said tie bar includes an interposer supported for movement between a first position aligned with aid tie bar and a second position misaligned with said tie bar; and electrically actuatable means for selectively moving said interposer to said first position whereby said backplate can be drawn toward said interposer to engage said interposer and tie bar for moving said tie bar to said extended position relative to said backplate.
 11. The head-positioning assembly of claim 10 wherein said latching means includes means secured to said tie bar defining a latch arm receptacle; a latch member, having a latch arm, mounted for pivotal movement; and electrically responsive means for pivoting said latch member to engage said latch arm in said receptacle wHen said tie bar is in said extended position.
 12. The head positioning assembly of claim 11 wherein said electrically responsive means includes a control cable having a jacket and a central cable therein and movable with respect thereto; and means mounting said control cable with said central cable engaged with said latch member. 